This invention relates to a gas leak detector apparatus and more particularly to a technique and apparatus for detecting gas leaks utilizing pressure transducers.
As is well known, at normal pressures and temperatures, the pressure of a gas is given by the ideal gas law PV=NRT where V is the volume occupied by N moles of the gas, P stands for pressure, R is the universal gas constant and T is the absolute temperature. As is known, a mole equals 6.times.10.sup.23 molecules of any substance.
There are many texts and articles existing in the prior art regarding theories of gas and the equation governing gas behavior. The ideal gas law is indicated above. One can of course understand that there is a need to determine whether or not there is a leak in a particular container or vessel which contains gas. The so-called leak detector is an extremely important device especially when one is dealing with obnoxious or poisonous gases as well as certain types of gases which are combustable or highly dangerous. It is, therefore, apparent that one needs a device which will detect a leak in a container.
Such a device should provide one with an accurate representation of the magnitude of the leak as well as the intensity of the same in regard to the escape of gas so that suitable alarms or suitable warnings can be given or that the overall amount or number of molecules or moles of the gas in the vessel can otherwise be ascertained.
Essentially, as indicated above, the concentration of combustable gases, for example, must be determined and controlled in manufacturing operations and other industrial situations for several reasons. These include safety reasons to avoid explosions by maintaining concentrations well below the lower explosive limit and also to avoid the toxic effects of most combustable gases on operating personnel. There is further concern regarding processing efficiency, and therefore one must maintain optimum concentrations for combustion and other chemical reactions where such gases may be used as well as for detection of faulty operating equipment and procedures.
In any event, the prior art is replete with a number of gas analyzers which all serve to monitor the concentration of gases. A very common device used employs a self-heated hot wire detector which is usually made of platinum. The wire also serves as a combustion catalyst, and where the combustable gas to be measured also contains air the mixture is fed to a hot wire detector whereupon combustion occurs. A temperature sensor such as a thermocouple may detect a temperature rise and this in turn is a measure of the concentration of the gas. More frequently, the electrical resistance of the hot wire itself is measured as the means for detecting temperature rise much as occurs in a typical electrical resistance thermometer. Where the sample does not contain an excess of oxygen then air or oxygen must be added to the sample in carefully controlled quantities but added well in excess of combustion requirements so that the reaction occuring within the detector will be limited only by the amount of combustable gases or vapors present.
Wheatstone bridge circuitry is generally used in these instruments. In any event, where a bridge circuit is used, the reference detector is also required. The reference gas may be air or the sample gas also may be used for these purposes. In other types of gas analyzers, the sample gas is burned in a small pilot flame where the temperature is detected by a thermocouple. The presence of combustables in the supply of gas to the pilot causes the flame temperature to increase proportionately with concentration. There are gas analyzers which are called thermal conductivity types, as different gases vary considereably in their ability to conduct heat. Such devices use hot wire gas analyzer cells where a typical cell is comprised of an electrically conductive elongated sensing element that is mounted coaxial inside a cylindrical chamber which contains the gas. By passage of an electrical current through the element, the cell is maintained at a temperature considerably higher than the cell wall. The equilibrium temperature is reached when all thermal losses from the wire are equalized by the electric power input to the element.
The difference of temperature between the element and the cell walls reflected by the temperature rise of the element at equilibrium is a function of electric power input and combined rate of heat loss from the wire by gaseous conduction, convection, radiation and conduction through the solid parts of the element. Thus proper cell design and geometry makes it possible to maximize the heat loss due to gaseous conduction. Thus a rise in the temperature of the element at constant electric power input is inversely related to the thermal conductivity of the gas within the cell. Normally, a Wheatstone bridge is used to measure resistance change of the sensing element.
In any event, suffice it to say, that there are many techniques employed in the prior art which essentially serve to monitor the concentrating of gases. Such techniques can of course be employed to determine whether or not a vessel containing a gas is subjected to a leak by knowing what the number of molecules are.
As one can see from the ideal gas law, changes in temperature result in changes in pressure and so on. Many of the prior art devices, as indicated above, suffer in that they are very complicated or require multiple components and are normally difficult to monitor and to utilize.
It is, therefore, an object of the present invention to provide and improved gas detecting apparatus which is simple and inexpensive to maintain or operate. It is a further object of the present invention to provide a gas leak detector apparatus, which utilizes a pressure transducer in a reliable and efficient manner, to determine any change in N, the number of moles of gas in a container.